The present invention relates to a resistance change memory and a forming method of a resistance change device.
Resistance change memories (ReRAM: Resistance RAM) have been known as a kind of volatile memories (for example, refer to: W. W. Zhuang, et al., “Novell Colossal Magnetoresistive Thin Film Nonvolatile Resistance Random Access Memory (RRAM)”, IEDM, 7.5, pp. 193-196, 2002 (Non-Patent Document 1),
G. -S. Park, et al., “Observation of electric-field induced Ni filament channels in polycrystalline NiOx film”, APL, Vol. 91, pp. 222103, 2007 (Non-Patent Document 2),
C. Yoshida et al., “High speed resistive switching in Pt/TiO2/TiN film for nonvolatile memory application” APL, Vol. 91, pp. 223510, 2007 (Non-Patent Document 3), and
M. Terai et al., “High Thermal Robust ReRAM with a New Method for Suppressing Read Disturb”, 2011 Symposium on VLSI Technology, Digest of Technical Papers, pp. 50-51, 2011 (Non-Patent Document 4)).
The resistance change memory uses a resistance change device as a memory cell and stores data based on the change of the resistance in a non-volatile manner.
As shown in FIG. 1, a typical resistance change device has a first electrode 110, a second electrode 120, and a resistance change layer 130 interposed between the first electrode 110 and the second electrode 120. By applying voltage between the first electrode 110 and the second electrode 120, the resistance value of the resistance change layer 130 can be changed thereby capable of rewriting data.
In the Non-Patent Document 1, a PCMO (Pr0.7Ca0.3MnO3) film and a YBCO (YBa2Cu3Oy) film are used as the resistance change layer 130.
In the Non-Patent Document 2, a polycrystal NiOx (x=1 to 1.5) film of about 50 nm thickness is used as the resistance change layer 130.
In the Non-Patent Document 3, a crystallite TiO2 film of 80 nm thickness is used as the resistance change layer 130.
In the Non-Patent Document 4, different materials are used for the first electrode 110 and the second electrode 120 (asymmetric electrode) with an aim of decreasing read disturb. For example, the material for the first electrode 110 is Ru and the material for the second electrode 120 is W.
When such a resistance change device is utilized, a treatment referred to as “forming” is necessary for initial setting. Forming is to form a conduction path referred to as “filament” in the resistance change layer 130 by application of a high voltage between the first electrode 110 and the second electrode 120. It is considered that the filament is formed by collection of defects in the resistance change layer 130.
As illustrated in FIG. 1, a filament 140 (conduction path) is formed in the resistance change layer 130 so as to connect the first electrode 110 and the second electrode 120. The state corresponds to “an ON state” in which the resistance of the resistance change device is low. After the forming, ON/OFF switching is possible.